This invention relates to a new therapeutic use of aminophosphonate compounds for lowering plasma and tissue levels of lipoprotein(a). In particular, this invention provides a new use of aminophosphonate derivatives, for the preparation of pharmaceutical compositions useful in the treatment of diseases or disorders associated with high plasma and tissue concentrations of lipoprotein(a); such as, for instance artherosclerosis, thrombosis, restenosis after angioplasty and stroke. This invention also provides a method for increasing thrombolysis and preventing thrombosis and a method of treatment of restenosis after angioplasty by administering to a patient in need thereof an aminophosphonate compound at a dose effective for lowering plasma and tissue lipoprotein(a) levels. In addition, this invention also provides a group of new aminophosphonate compounds for use in the above mentioned uses and compositions.
Recent epidemiologic studies have shown a strong association between elevated lipoprotein(a) [Lp(a)] plasma levels and the occurrence of coronary heart disease, stroke and peripheral artery disease. Lp(a) is now recognized as an independent risk factor for cardiovascular diseases; in addition its role in promoting thrombosis by decreasing thrombolysis is increasingly acknowledged, see for instance xe2x80x9cLipoprotein(a) as A Risk Factor for Preclinical Atherosclerosisxe2x80x9d P. J. Schreiner, J. D. Morrisett, A. R. Sharrett, W. Patsch, H. A. Tyroler, K. Wu and G. Heiss; Arteriosclerosis and Thrombosis 13 p. 826-833 (1993); xe2x80x9cDetection and Quantification of Lipoprotein(a) in the Arterial Wall of 107 Coronary Bypass Patientsxe2x80x9d M. Rath, A. Niendorf, T. Reblin, M. Dietel, H. J. Krebber and U. Beisiegel; Arteriosclerosis 9, p. 579-592 (1989); and xe2x80x9cLipoprotein(a): Structure, Properties and Possible Involvement in Thrombogenesis and Atherogenesisxe2x80x9d A. D. MBewu and P. N. Durrington; Atherosclerosis 85, p. 1-14 (1990). The potential of thrombosis involvement in vessel occlusion and acute cardiovascular syndrome is being increasingly recognized. One of the mechanisms that mediate thrombosis associated with atherosclerotic plaque rupture involves elevated levels of lipoprotein(a). The structure of Lp(a) consists of a low-density lipoprotein (LDL)-like particle with a glycoprotein, apolipoprotein(a) [apo(a)] that is linked via a disulfide bridge to the apo B-100 moiety of the LDL. Structurally there is striking analogy between apo(a) and plasminogen, the precursor of plasmin which cleaves fibrin to dissolve blood clots. However, unlike plasminogen apo(a) is not a substrate for plasminogen activators. This structural resemblance has led researchers to postulate and later demonstrate that apo(a) interferes with the normal physiological function of plasminogen, leading to a potential thrombogenic activity of Lp(a) see for instance:
xe2x80x9cActivation of Transforming Growth Factor-xcex2 is Inversely Correlated with Three Major Risk Factors for Coronary Artery Disease: Lipoprotein(a), LDL-Cholesterol and Plasminogen Activator Inhibitor-1xe2x80x9d, A. Chauhan, N. R. Williams, J. C. Metcalfe, A. A. Grace, A. C. Liu, R. M. Lawn, P. R. Kemp, P. M. Schofield and D. J. Grainger; Circulation, Vol 90, No. 4, Part 2, p. I-623 (1994); and
xe2x80x9cInfluence of Human Apo(a) Expression on Fibrinolysis in vivo in Trangenic Micexe2x80x9d T. M. Palabrica, A. C. Liu, M. J. Aronovitz, B. Furie, B. C. Furie and R. Lawn; Circulation, Vol 90, No. 4, Part 2, p. I-623 (1994).
On the basis of its suspected thrombogenic activity, Lp(a) has also been implicated in peripheral artery disease, in particular stroke. Recently clinicians have shown that serum Lp(a) levels were significantly higher in stroke patients than in a reference normal population:
xe2x80x9cLp(a) Lipoprotein in Patients with Acute Strokexe2x80x9d K. Asplund, T. Olsson, M. Viitanen and G. Dahlen; Cerebrovasc. Diseases 1, p. 90-96 (1991).
Restenosis following percutaneous transluminal angioplasty is a common complication occurring in up to 40% of cases within 3-6 months of the intervention. The main cause for restenosis is believed to be abnormal vascular smooth muscle cell activation and proliferation. The proof that high plasma Lp(a) levels are associated with smooth muscle cell proliferation and activation was established in vitro and in vivo by the two following studies:
xe2x80x9cProliferation of Human Smooth Muscle Cells Promoted by Lipoprotein(a)xe2x80x9d D. J. Grainger, H. L. Kirschenlohr, J. C. Metcalfe, P. L. Weissberg, D. P. Wade and R. M. Lawn; Science, Vol 260, p.1655-1658 (1993); and
xe2x80x9cActivation of Transforming Growth Factor-xcex2 is Inhibited by Apolipoprotein (a) in vivoxe2x80x9d, D. J. Grainger, P. R. Kemp, A. C. Liu, R. M. Lawn and J. C. Metcalfe; Circulation, Vol 90, No. 4, Part 2, p. I-623 (1994).
This observation has led to a hypothesis that associates elevated plasma Lp(a) levels with an increased incidence of restenosis. The hypothesis was confirmed by the results of a recent clinical study showing that, in patients with high plasma Lp(a) levels, a reduction of Lp(a) levels by more than 50% by LDL-apheresis significantly reduced the restenosis rate; see for instance:
xe2x80x9cEffectiveness of LDL-Apheresis in Preventing Restenosis After Percutaneous Transluminal Coronary Angioplasty (PTCA): LDL-Apheresis Angioplasty Restenosis Trial (L-ART)xe2x80x9d H. Yamaguchi, Y. J. Lee, H. Daida, H. Yokoi, H. Miyano, T. Kanoh, S. Ishiwata, K. Kato, H. Nishikawa, F. Takatsu, Y. Kutsumi, H. Mokuno, N. Yamada and A. Noma; Chemistry and Physics of Lipids, Vol 67/68, p. 399-403(1994).
The above discussion has established the rationale for decreasing plasma Lp(a) in patients at risk with elevated levels ( greater than 20-30 mg/dl). The Lp(a) concentration in individuals appears to be highly determined by inheritance and is hardly influenced by dietary regimes. Various hormones (i.e. steroid hormones, growth hormones, thyroid hormones) have been shown to regulate plasma levels of Lp(a) in man. Of particular interest, drugs which effectively lower LDL such as the bile acid sequestrant cholestyramine or the HMGCoA reductase inhibitors lovastatin or pravastatin do not affect Lp(a) levels. The drugs of the fibrate family: clofibrate or bezafibrate and the antioxidant drug probucol are equally ineffective. The only drug reported to lower Lp(a) is nicotinic acid. However at the high doses necessary for efficacy (4 g/day) nicotinic acid has several serious side-effects which preclude its wide use: flushing, vasodilation and hepatotoxicity. Therefore the medical need to lower elevated Lp(a) plasma levels, an independent risk factor for cardiovascular disease, is still unmet.
In contrast to LDL, Lp(a) exists only in mammals high in the evolutionary scale (humans and non human primates) and is exclusively synthesized by the liver cells. Cynomolgus monkeys possess Lp(a) that is similar to human Lp(a), including possession of the unique apolipoprotein apo(a). This primate offers an experimental opportunity for studying the synthesis of Lp(a) and the role of Lp(a) in atherosclerosis and thrombosis. Primary cultures of cynomolgus monkey hepatocytes have been selected as the in vitro test for screening aminophosphonate derivatives of formula (I) for their ability to modulate Lp(a) levels. Prior to screening, this assay system had been validated by testing as reference products nicotinic acid and steroid hormones which are known to lower Lp(a) in man.
The present invention relates to the unexpected discovery that aminophosphonate derivatives are effective for lowering plasma and tissue lipoprotein(a). Accordingly, in a first aspect, the present invention provides for the use of a compound of formula (I): 
where:
X1, X2, which may be identical or different, are H, a straight or branched alkyl or alkoxy group having from 1 to 8 carbon atoms, a hydroxy group or a nitro group,
X3 is H, an alkyl group from 1 to 4 carbon atoms, X3O and one of the two other substituents X1 or X2 may form an alkylidene dioxy ring having from 1 to 4 carbon atoms,
R1, R2, identical or different, are H, a straight or branched alkyl group having from 1 to 6 carbon atoms,
B is CH2, CH2xe2x80x94CH2 or CHxe2x95x90CH,
n is zero or 1,
Z is H, a straight or branched alkyl group having from 1 to 8 carbon atoms, an acyl group R3xe2x80x94CO where R3 is an alkyl group from 1 to 4 carbon atoms, a perfluoroalkyl group from 1 to 4 carbon atoms,
A is H, CH2xe2x80x94CHxe2x95x90CH2, a straight, branched or cyclic alkyl group having from 1 to 8 carbon atoms, or is selected from the following groups: 
where k is an integer from 2 to 4, m is 0 or an integer from 1 to 5, X4, X5, X6, identical or different, are H, a straight or branched alkyl or alkoxy group from 1 to 8 carbon atoms, a hydroxy, trifluoromethyl, nitro, amino, dimethylamino, diethylamino group, a halogen atom (F, Cl, Br, I), X4 and X5 may form an alkylidendioxy ring having from 1 to 4 carbon atoms, X7 is H or CH3, R is a straight or branched alkyl group having from 1 to 6 carbon atoms, an aryl or arylalkyl group from 6 to 9 carbon atoms;
or a pharmaceutically acceptable salt thereof;
in the manufacture of a medicament for lowering plasma and tissue lipoprotein(a).
European Patent Application EP 0""559""079A (1993) [corresponding to the U.S. Pat. No. 5,424,303] discloses compounds of formula (I) as well as their use in decreasing plasma cholesterol and blood peroxides.
Preferred compounds of formula (I) for use in the manufacture of a medicament for lowering plasma and tissue lipoprotein(a) are those of the formula (Ia): 
where B, R1, R2, X1, X2, X3, X4, Z, n and m are as hereinbefore defined;
or a pharmaceutically acceptable salt thereof.
Certain compounds within the scope of formula (Ia) are novel and are particularly useful in lowering plasma and tissue lipoprotein(a).
Accordingly, in a further aspect, this invention provides aminophosphonate derivatives of formula (Ia) where:
X1 is H, C(1-8)alkyl or C(1-8)alkoxy;
X2 is C(1-8)alkyl or C(1-8)alkoxy;
X3 is H, C(1-4)alkyl, or X3O and one of the two other substituents X1 or X2 may form an alkylidene dioxy ring having from 1 to 4 carbon atoms;
R1, R2, which may be identical or different, are H or C(1-6)alkyl;
B is CH2xe2x80x94CH2, CHxe2x95x90CH or CH2;
n is zero or 1;
Z is H or C(1-8)alkyl;
m is an integer from 0 to 5;
X4 is H, C(1-8)alkyl, C(1-8)alkoxy, or halo;
and the pyridyl ring is attached by the ring carbon xcex1- or xcex2- to the nitrogen (2- or 3-pyridyl);
or a salt, preferably a pharmaceutically acceptable salt, thereof; and excluding:
Diethyl xcex1-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-(3-pyridyl)aminomethylphosphonate;
Diethyl xcex1-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-(2-picolyl)aminomethylphosphonate;
Diethyl xcex1-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-(3-picolyl)aminomethylphosphonate;
Diethyl xcex1-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-methyl-N-(3-picolyl)aminomethylphosphonate;
Diethyl xcex1-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-(2-pyridylethyl)aminomethylphosphonate, and
Diethyl xcex1-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-(4-picolyl)aminomethylphosphonate.
Suitably, X1 is H, C(1-4)alkyl or C(1-4)alkoxy, preferably C(1-3)alkyl or C(1-3)alkoxy, more preferably hydrogen, methyl or methoxy.
Suitably, X2 is C(1-4)alkyl or C(1-4)alkoxy, preferably C(1-3)alkyl or C(1-3)alkoxy, more preferably methyl or methoxy.
Suitably, X1 and X2 are both alkoxy or one of X1 and X2 is alkyl and the other is alkoxy, or one of X1 and X2 is C(1-4)alkyl and the other of X1 and X2 is C(1-3)alkyl.
Suitable combinations of X1 and X2 include methoxy and methoxy, methoxy and methyl, n-propyl or isobutyl, methyl and methyl or t-butyl, respectively.
Preferably, X3 is hydrogen.
Preferably, (B)n is a direct bond.
Preferably, R1 and R2 is each a C(1-3)alkyl group, more preferably, a C2 or C3 alkyl group, in particular R1 and R2 is ethyl or isopropyl.
Preferably, Z is hydrogen.
Preferably, X4 is hydrogen or methyl which is preferably on the ring carbon adjacent to N.
Preferably, the pyridyl ring is attached by the ring carbon xcex2- to the nitrogen (3-pyridyl).
When used herein, the terms xe2x80x98alkylxe2x80x99 and xe2x80x98alkoxyxe2x80x99 include both straight and branched groups, for instance, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, s-butyl, t-butyl, etc.
Preferred compounds of formula (Ia) include:
Diisopropyl xcex1-(4-hydroxy-3-methoxy-5-methylphenyl)-N-(3-pyridyl)-aminomethylphosphonate;
Diisopropyl xcex1-(3,5-dimethoxy-4-hydroxyphenyl)-N-(3-pyridyl)-aminomethylphosphonate;
Diethyl xcex1-(3-methyl-4-hydroxy-5-t-butylphenyl)-N-(3-pyridyl)-aminomethylphosphonate;
Diethyl xcex1-(3,5-dimethoxy-4-hydroxyphenyl)-N-(3-pyridyl)-aminomethylphosphonate; and
Diethyl xcex1-(3,5dimethyl-4-hydroxyphenyl)-N-(3pyridyl)-aminomethylphosphonate.
Independently from the previously published activity, the present invention relates to the unexpected discovery that aminophosphonate derivatives of formula (I) are effective for decreasing Lp(a) production by primary cultures of Cynomolgus monkey hepatocytes. Lp(a) of these primates is similar in immunologic properties to human Lp(a) and occurs in an almost identical frequency distribution of plasma concentrations, see for instance:
xe2x80x9cPlasma Lipoprotein(a) Concentration is Controlled by Apolipoprotein(a) Protein Size and the Abundance of Hepatic Apo(a) mRNA in a Cynomolgus Monkey Modelxe2x80x9d, N. Azrolan, D. Gavish and J. Breslow; J. Biol. Chem., Vol 266, p. 13866-13872 (1991).
Therefore the compounds of this invention are potentially useful for decreasing Lp(a) in man and thus provide a therapeutic benefit.
In particular, this invention provides a new therapeutic use for aminophosphonate compounds of formula (I) as Lp(a) lowering agents. Diseases associated with elevated plasma and tissue levels of lipoprotein(a) include, for instance, coronary heart disease, peripheral artery disease, intermittent claudication, thrombosis, restenosis after angioplasty, extracranial carotid atherosclerosis, stroke and atherosclerosis occuring after heart transplant.
The recently discovered Lp(a) lowering activity of the aminophosphonates of formula (I) is independent from their previously reported pharmacological activities of decreasing plasma cholesterol and blood peroxides. Recent clinical studies have shown that neither the hypocholesterolemic drug pravastatin nor the antioxidant drug probucol can decrease Lp(a) levels in man. See for example:
xe2x80x9cSerum Lp(a) Concentrations are Unaffected by Treatment with the HMG-CoA Reductase Inhibitor Pravastatin: Results of a 2-Year Investigationxe2x80x9d H. G. Fieseler, V. W. Armstrong, E. Wieland, J. Thiery, E. Schiltz, A. K. Walli and D. Seidel; Clinica Chimica Acta, Vol 204, p. 291-300 (1991); and
xe2x80x9cLack of Effect of Probucol on Serum Lipoprotein(a) Levelsxe2x80x9d, A. Noma; Atherosclerosis 79, p. 267-269 (1989).
For therapeutic use the compounds of the present invention will generally be administered in a standard pharmaceutical composition obtained by admixture with a pharmaceutical carrier selected with regard to the intended route of administration and standard pharmaceutical practice. For example, they may be administered orally in the form of tablets containing such excipients as starch or lactose, or in capsule, ovules or lozenges either alone or in admixture with excipients, or in the form of elixirs or suspensions containing flavouring or colouring agents. They may be injected parenterally, for example, intravenously, intramuscularly or subcutaneously. For parenteral administration, they are best used in the form of a sterile aqueous solution which may contain other substances, for example, enough salts or glucose to make the solution isotonic with blood. The choice of form for administration as well as effective dosages will vary depending, inter alia, on the condition being treated. The choice of mode administration and dosage is within the skill of the art.
The compounds of structure (I) and their pharmaceutically acceptable salts which are active when given orally can be formulated as liquids, for example syrups, suspensions or emulsions or as solids for example, tablets, capsules and lozenges. A liquid formulation will generally consist of a suspension or solution of the compound or pharmaceutically acceptable salt in a suitable liquid carrier(s) for example, ethanol, glycerine, non-aqueous solvent, for example polyethylene glycol, oils, or water with a suspending agent, preservative, flavouring or colouring agents.
A composition in the form of a tablet can be prepared using any suitable pharmaceutical carrier(s) routinely used for preparing solid formulations. Examples of such carriers include magnesium stearate, starch, lactose, sucrose and cellulose.
A composition in the form of a capsule can be prepared using routine encapsulation procedures. For example, pellets containing the active ingredient can be prepared using standard carriers and then filled into a hard gelatin capsule; alternatively, a dispersion or suspension can be prepared using any suitable pharmaceutical carrier(s), for example aqueous gums, celluloses, silicates or oils and the dispersion or suspension then filled into a soft gelatin capsule.
Typical parenteral compositions consist of a solution or suspension of the compound or pharmaceutically acceptable salt in a sterile aqueous carrier or parenterally acceptable oil, for example polyethylene glycol, polyvinyl pyrrolidone, lecithin, arachis oil or sesame oil. Alternatively, the solution can be lyophilised and then reconstituted with a suitable solvent just prior to administration.
A typical suppository formulation comprises a compound of structure (I) or a pharmaceutically acceptable salt thereof which is active when administered in this way, with a binding and/or lubricating agent such as polymeric glycols, gelatins or cocoa butter or other low melting vegetable or synthetic waxes or fats.
Preferably the composition is in unit dose form such as a tablet or capsule.
Each dosage unit for oral administration contains preferably from 1 to 250 mg (and for parenteral administration contains preferably from 0.1 to 25 mg) of a compound of the structure (I) or a pharmaceutically acceptable salt thereof calculated as the free base.
The pharmaceutically acceptable compounds of the invention will normally be administered to a subject in a daily dosage regimen. For an adult patient this may be, for example, an oral dose of between 1 mg and 500 mg, preferably between 1 mg and 250 mg, or an intravenous, subcutaneous, or intramuscular dose of between 0.1 mg and 100 mg, preferably between 0.1 mg and 25 mg, of the compound of the structure (I) or a pharmaceutically acceptable salt thereof calculated as the free base, the compound being administered 1 to 4 times per day.
Compounds of formula (I) may be prepared according to the processes described in European Patent Application EP 0 559 079-A (1993[corresponding to the U.S. Pat. No. 5,424,303]. This process which has two variants is shown in the following general scheme: 
Variant 1 is used when Z is H, i.e. when the starting compound is a primary amine. Briefly, the aminophosphonates of formula (I) are prepared by nucleophilic addition of a dialkyl phosphite or its sodium salt obtained in situ by the reaction of dialkyl phosphite and sodium hydride on the imine obtained by condensation of the appropriate aldehyde and a primary amine.
Variant 2 is used when Z is not H, i.e. when the starting compound is a secondary amine. In this case, the aminophosphonates of formula (I) are prepared by reacting equimolar amounts of the appropriate aldehyde and the secondary amine and a dialkyl phosphite. The reaction is advantageously carried out in the presence of p-toluenesulfonic acid as a catalyst in a hydrocarbon solvent such as benzene or toluene with concomittant elimination of water, for instance, by using a Dean-Stark apparatus.
Novel compounds of formula (Ia) in which Z is hydrogen may be prepared by a process which comprises treating an imine of formula (II): 
in which B, X1, X2, X3, X4, m and n are as hereinbefore defined;
with a phosphite compound of formula (III):
HPO(OR1)(OR2)xe2x80x83xe2x80x83(III)
in which R1 and R2 are as hereinbefore defined; or a trialkyl silyl derivative thereof, preferably the trimethyl silyl phosphite, or a metal salt thereof, for instance the sodium salt, formed in situ by treatment of the compound of formula (III) with a suitable base, for instance sodium hydride, ethoxide or methoxide.
The reaction may be carried out in the presence or absence of a catalyst. Suitable catalysts include amine such as diethylamine or triethylamine. The reaction may be carried out in the absence or presence of a solvent. Suitable solvents include petroleum ether, benzene, toluene, diethyl ether, tetrahydrofuran, 1,2-dimethoxyethane. Suitable reaction temperatures are in the range 30 to 140xc2x0 C.
The imine compound of formula (II) may be obtained by condensing an aldehyde compound of formula (V): 
in which B, X1, X2, X3 and n are as hereinbefore defined;
with a primary amine of formula (VI):
H2NAxe2x80x83xe2x80x83(VI)
in which A is as hereinbefore defined;
under imine forming conditions.
Suitably, the condensation may be effected with or without a catalyst in a solvent such as ether, tetrahydrofuran, benzene, toluene or ethanol. Suitable catalysts include molecular sieve, an acid such as glacial acetic acid, p-toluene sulphonic acid, thionyl chloride, titanium tetrachloride, boron trifluoride etherate, or a base such as potassium carbonate. The reaction is suitably carried out at a temperature in the range 0xc2x0 C. to the boiling point of the solvent being used. For less reactive amines/aldehydes, the reaction may be usefully carried out in a Dean-Stark apparatus.
Novel compounds of formula (Ia) in which Z is not hydrogen may be prepared by a process which comprises treating equimolar amounts of an aldehyde of formula (V), a secondary amine of formula (VII):
HNZAxe2x80x83xe2x80x83(VII)
in which Z is a C(1-8)alkyl group and A is as hereinbefore defined; and
a phosphite of formula (III), suitably in the presence of p-toluenesulfonic acid as a catalyst, in a hydrocarbon solvent such as petroleum ether, benzene, toluene or xylene, at a temperature between ambient temperature and the boiling point of the solvent being used, and with concomittant elimination of water, for instance, by using a Dean-Stark apparatus.
Compounds of formula (Ia) in which m is not zero may also be prepared by a process which comprises treating a compound of formula (VIII): 
in which B, R1, R2, X1, X2, X3 and n are as hereinbefore defined;
an aldehyde of formula (IX): 
in which m is an integer from 1 to 5 and X4 is as hereinbefore defined;
under reductive amination conditions.
Suitable such conditions include carrying out the reaction in the presence of sodium cyanoborohydride in an alcoholic solvent, preferably methanol, at a pH between 3 to 6 and at a temperature between 0xc2x0 C. and 25xc2x0 C.
A compound of formula (VIII) may be obtained according to the process hereinbefore described for a compound of formula (Ia) from an aldehyde of formula (V), a secondary amine of formula (VII) in which Z is protecting group which can be removed by hydrogenolysis, for instance an xcex1 substituted benzyl or bezyloxycarbonyl and a phosphite of formula (III). This forms an intermediate which is then subjected to hydrogenolysis according to standard conditions, to give a compound of formula (VIII).
Through their amino function, the aminophosphonate ester (I) can form salts of inorganic acids such as HCl, H2SO4 or with organic acids such as oxalic acid, maleic acid, sulfonic acids, etc. An example of hydrochloride salt of aminophosphonate (I) is provided (example 5). All these salts are integral part of this invention.
Compounds of structure (I) are racemates as they have at least one chiral center which is the carbon atom in position alpha to the phosphonate group. The compounds (I) therefore exist in the two enantiomeric forms. The racemic mixtures (50% of each enantiomer) and the pure enantiomers are comprised in the scope of this application. In certain cases, it may be desirable to separate the enantiomers.
In a further aspect, the present invention provides a process for the enantiomeric synthesis of a derivative of formula (I) which process comprises treating either of the (+) or (xe2x88x92) enantiomer of the xcex1-substituted aminomethylphosphonate of formula (X): 
in which B, R1, R2, X1, X2, X3 and n are as hereinbefore defined;
with an aldehyde of formula (XI):
R3xe2x80x94CHOxe2x80x83xe2x80x83(XI)
in which R3 is as hereinbefore defined;
under reductive amination conditions.
Suitable such conditions include carrying out the reaction in the presence of sodium cyanoborohydride in an alcoholic solvent, preferably methanol, at a pH between 3 to 6 and at a temperature between 0xc2x0 C. and 25xc2x0 C.
The key xcex1-substituted primary aminomethylphosphonate of formula (X) is obtained by treating an aldehyde of formula (V), as hereinbefore defined, with (+) or (xe2x88x92)xcex1-methylbenzylamine to form an intermediate imine which is then reacted with a phosphite ester HPO(OR1)(OR2) to give a mixture of diastereoisomers which may be separated by conventional techniques, for instance fractional crystallisation or chromatography. Hydrogenolysis can then be used to remove the benzyl group from nitrogen, to give the xcex1-substituted primary aminomethyl-phosphonate of formula (X). This approach is illustrated by the preparation of enantiomers of compounds No. 7 and 15 of Table 1. Alternately. the resolution of the aminophosphonate racemates can be effected by preparative chiral chromatography, in particular chiral HPLC. The experimental conditions for chromatographic separation of enantiomers of compound No. 20 are provided. With either separation method, final enantiomeric purity can be ascertained by measuring the specific rotations of the separated isomers.
The structure of compounds of formula (I) were established by their elemental analysis, their infrared (IR), mass (MS) and nuclear magnetic resonance (NMR) spectra The purity of the compounds was checked by thin layer, gas liquid or high performance liquid chromatographies.
The invention is further described in the following examples which are intended to illustrate the invention without limiting its scope. In the tables, n is normal, i is iso, s is secondary and t is tertiary. In the description of the NMR spectra, respectively s is singlet, d doublet, t triplet and m multiplet TsOH is p-toluenesulfonic acid monohydrate. The temperatures were recorded in degrees Celsius and the melting points are not corrected. In the measurement of optical activity, an enantiomer which rotates the plane of polarized light to the right is called dextrorotatory and is designated (+) or (D). Conversely, levorotatory defines an enantiomer which rotates the plane of polarized light to the left, designated (xe2x88x92) or (L). Unless otherwise indicated, the physical constants and biological data given for aminophosphonates of formula (I) refer to racemates.